Multi-factor authentication (MFA) is a scheme for controlling access to computers in which a user is only granted access after presenting separate pieces of identification evidence to an authentication system. Multi-factor authentication schemes may be two-factor (e.g., requiring two pieces of information), three-factor, or more. Factors are conventionally broken out into rough categories of knowledge, possession, and inherence. In other words, factors are representative of what one knows (knowledge), what one has (possession), and what one is (inherence). Examples of knowledge factors include usernames, passwords, personal identification numbers (PINs), and the like. Examples of possession factors include an RFID tag, a pass card, and the like. Examples of inherence factors include fingerprints, retinal scans, and other biometric data.